Purification of metallurgical grade silicon

Abstract

There is disclosed a process for preparing ultra pure silicon from metallurgical grade silicon, which comprises (a) continuously passing powdered and acid-leached metallurgical grade silicon through an induction plasma; (b) quenching said treated particles whereby upon solidification of the molten particles, a portion of the impurities therein migrates to the surface of the granules obtained; (c) acid-leaching the surface impurities of the granules obtained in step (b); and (d) after drying the granules obtained, repeating steps (a), (b) and (c) until a silicon of the desired purity is obtained.

I claim: 
     
       1. Process for preparing ultra pure silicon which comprises: (a) continuously passing powdered and acid-leached metallurgical grade silicon through an induction plasma to melt the silicon;   (b) quenching said molten silicon particles whereby upon solidification of the molten particles, a portion of the impurities therein migrates to the surface of the granules obtained;   (c) acid-leaching the surface impurities of the granules obtained in step (b); and   (d) after drying the granules obtained, repeating steps (a), (b), and (c) until a silicon of the desired purity is obtained.   
     
     
       2. The process of claim 1, wherein the acid leaching comprises a first treatment with boiling hydrochloric acid, and after filtration a second treatment with hydrofluoric acid. 
     
     
       3. The process of claim 1 wherein one of the impurities is iron and steps (a), (b), and (c) are repeated until the iron content is reduced. 
     
     
       4. The process of claim 3 wherein the acid leaching comprises a first treatment with boiling hydrochloric acid, and after filtration a second treatment with hydrofluoric acid. 
     
     
       5. The process of claim 1 wherein the plasma treatment is carried out in an inductively coupled radio frequency torch.